All green plants synthesize their food through the process of photosynthesis and water is an essential component required by the leaves for photosynthesis. Xylems carry water from the roots to the other parts of the plant. Leaves play a vital role in this biological process and stem transports the prepared food to different parts of the plant. Root system plays a significant role in the plant’s survival as they help in transferring water and other minerals. Hence, various parts of plants help in carrying out daily life processes.

Like all living organism, plants too require an excretory system to discharge excess wastes from their body and it is the crucial life process as photosynthesis and transportation.

What is Transpiration?

Transpiration is the biological process by which water is lost in the form of water vapor from the aerial parts of the plants.

During the process of transpiration, water molecules are carried through plants tissues from roots to the small pores on the underside of leaves called stomata, where it changes to vapor and is released to the atmosphere.


Factors affecting Transpiration

The cellular factors affecting the rate of transpiration are:

  1. Orientation of leaf,
  2. The water status of the plant,
  3. Structural Peculiarities of leaf,
  4. Total number and distribution of stomata in a leaf.

The environmental factors affecting the rate of transpiration are:

  1. Light,
  2. Humidity,
  3. Temperature,
  4. Atmospheric pressure,
  5. Wind speed or velocity.

When water evaporates through the leaves, a pull is created through the xylem, and water moves back to the leaves.

The ascent of sap that is driven by transpiration depends on the following properties of water:

  • Cohesion – This is the mutual attraction between molecules of water.
  • Adhesion – The attraction of water molecules towards polar surfaces.
  • Surface tension – The molecules of water are more attracted to each other in the liquid phase than in the gas phase.

Opening and Closing of Stomata

Opening and Closing of Stomata

Stomata consist of a pair of guard cells with an aperture in between. It remains open during the daytime and is closed at night. The reason for the opening and closing of this structure is the turgidity of guard cells. The interior wall of the guard cells present towards the aperture is dense and flexible. The stomata open when the turgidity of the guard cells increases. The exterior walls bulge out and the interior walls form a crescent shape. The orientation of the microfibrils in the guard cells also plays an important role in the opening of the stoma. The radial orientation of the microfibrils makes it easier for the stoma to open. The stomata close when the turgidity of the guard cells decreases due to the water loss and the interior walls form a crescent shape retrieve their original shape.

In dicots, the lower side of leaves have more stomata while in monocots, both the sides have an equal number of stomata.

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Practise This Question

Xylem conducts food and phloem conducts water in the plant.